HWPOISON: detect free buddy pages explicitly

Most free pages in the buddy system have no PG_buddy set.
Introduce is_free_buddy_page() for detecting them reliably.

CC: Nick Piggin <npiggin@suse.de>
CC: Mel Gorman <mel@linux.vnet.ibm.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59d2e88fb47c..6867b4d391fd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5081,3 +5081,24 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
         spin_unlock_irqrestore(&zone->lock, flags);
 }
 #endif
+
+#ifdef CONFIG_MEMORY_FAILURE
+bool is_free_buddy_page(struct page *page)
+{
+        struct zone *zone = page_zone(page);
+        unsigned long pfn = page_to_pfn(page);
+        unsigned long flags;
+        int order;
+
+        spin_lock_irqsave(&zone->lock, flags);
+        for (order = 0; order < MAX_ORDER; order++) {
+                struct page *page_head = page - (pfn & ((1 << order) - 1));
+
+                if (PageBuddy(page_head) && page_order(page_head) >= order)
+                        break;
+        }
+        spin_unlock_irqrestore(&zone->lock, flags);
+
+        return order < MAX_ORDER;
+}
+#endif